Concrete shell construction method

ABSTRACT

A shell structure construction method utilizing a plurality of anchored and laterally connected pre-cast reinforced concrete shells, each of these subject shells has a specific shape in which the shell walls are defined by an inverted catenary shape or alternatively by other efficient geometric shapes. An improved joint support mechanic includes a combination of fastener elements and a plurality of post tensioned cable systems disposed between and connecting contiguous shell elements. This construction method is suitable for manufacturing and implementing severe storm shelters used during tornadoes and other severe weather events.

BACKGROUND OF THE INVENTION

Tornadoes are a most destructive force of nature. Their measurementscale ranges from a low EF0 to EF5. EF0 storms have winds of 72 mphwhile EF5 storms have winds in excess of 318 mph. The combined effectsof wind driven projectiles and wind forces are the destructive forcesexerted by a tornado.

EF5 damage represents the upper limit of tornado power, and destructionis almost always total. An EF5 tornado pulls well-built homes off theirfoundations and into the air before shredding them, flinging thewreckage for miles and sweeping the foundation clean. Very littlerecognizable structural debris is generated by EF5 damage, with mostmaterials reduced to a coarse mix of small, granular particles anddispersed evenly across the tornado's damage path. Large, multi-tonsteel frame vehicles and farm equipment are often mangled beyondrecognition and deposited miles away or reduced entirely tounrecognizable component parts. The official description of this damagehighlights the extreme nature of the destruction, noting that“incredible phenomena will occur”; historically, this has included suchawesome displays of power as twisting skyscrapers, leveling entirecommunities, and stripping asphalt from roadbeds. Despite their relativerarity, the damage caused by EF5 tornadoes represents adisproportionately extreme hazard to life and limb—since 1950 in theUnited States, only 58 tornadoes (0.1% of all reports) have beendesignated F5 or EF5, and yet these have been responsible for more than1,300 deaths and 14,000 injuries (21.5% and 13.6%, respectively).

Any construction system made to survive in this hostile environment andto keep its occupants safe must provide a level of safety that issuperior comparable to the existing structures and be available to amajority of the population at a reasonable cost. It should also providefor a secure personal feeling without increasing the individual anxietyand claustrophobic fear which some people develop in such trying andemotional circumstances. For instance many people have a primordial fearof going underground, especially during a time of severe duress. Ashelter concept and means are needed to mitigate the fears ofindividuals when using these shelters.

On May 3, 1999 a tornado in Moore, Okla. was measured by Doppler radarat 302 mph. At this speed the damage to structures is intense. Lifethreatening flying projectiles present a clear and present danger topeople. However, the projectiles do not actually fly at the measuredwind speed but usually at about a maximum level equal to ⅓ of thatmeasured wind velocity. Adequate protection is necessary to protect theindividual from this debris and also to maintain the integrity of thestructure in which the individual is waiting out the storm.

SPECIFICATION

Further compounding the challenge of the overall design and constructionobjectives of structures is the observation that cost, safety andpsychological effects are very important to most homeowners. Forexample, an affordable cost combination with structural integrity isvery high on the requirement list of many people. People need flexiblealternatives to current shelter designs and which can still provide asense of security and allow for ease of use by the typical individual. Adesign criterion as previously mentioned, the cost efficient use ofshelter floor space is also an ever-growing concern, particularly asbuilding costs continue to escalate. The circular floor concept embodiedin this invention maximizes the person capacity number for a given floorspace area.

Meeting these objectives often requires improved technology, improveddesign, and better understanding of the psychology of the human behaviorin stressful situations. Conventional severe storm construction methodsdo not adequately address all the problems that need to be solved in thearea of severe wind weather survival.

What is needed in the art is a shelter and a construction method that:

-   -   1. Utilizes better and more effective building technology to        provide a demonstrably structurally stronger and lighter in        design, also to minimize total material usage, and still produce        an intrinsically safer shelter;    -   2. Provides a comparatively more economical use of available        materials to more inexpensively design and install the shelter        that meets the affordability criteria of the general public;    -   3. Allows the standardization of manufacture and construction        procedures in order to use a wide range of workers of varying        competency levels during the construction phase;    -   4. Can be used to rapidly deploy the structures across a wide        range of regional locations: rural, urban or suburban;    -   5. Allows for easy transportation of the materials and        sub-assemblies of the shelter structures by using existing        trucks—large or small in size, or by rail or barge type        transportation;    -   6. Meets the social and personal acceptability criteria of the        populace, some of whom have had an individual phobias and fears        of going below ground during the inclement weather that is        associated with tornado-like events;    -   7. Meets the requirements of regulatory bodies and agencies like        FEMA and state, municipal and regional bodies.    -   8. Provides for maximum person occupancy per unit area of floor        space.

Thus, an improved shelter construction method that provides greaterphysical security to the occupants during critical and the verydestructive tornadic events, allows more rapid, time efficient and morestreamlined construction procedures, provides a more cost effective anda more occupant-friendly and user-preferable safety environment comparedto conventional methods of shelter design and use is desired. The novelshelter construction method implements a plurality of specially designedand implemented pre-fabricated concrete shells along with the necessarystructural and tensioning subassemblies to provide the stability andphysical survivability of the construction unit during severe windevents even up to EF-5 tornado level in order to keep the occupants safeand with a minimum level of fear for their personal safety during thewind event.

Through the discussions, below, it shall be shown that the shelter andconstruction disclosed herein, said construction is well suited for asafe system in tornadic conditions and other severe wind events.

SUMMARY OF THE INVENTION

The present invention relates to the construction of a shelter thatkeeps occupants safe during a major wind event like a tornado, hurricaneor a major weather disturbance.

Particularly, the present invention provides for the utilizing advancedbuilding technology to design, develop and construct a shelter systemthat by virtue of its structural design with specialized reinforcedconcrete shells using inverted catenary models and the integration ofcompressive tensioned assemblies into the structure, allows for alighter weight units which are as strong as existing storm shelters on aweight basis.

The shells which form the basic construction elements of the proposedinvention are designed to maximize the structural integrity of theshelter. Each shell is designed and constructed with precisioncomparable to that of a manufactured article. It is a feature of thisinventive process wherein remote offsite manufacturing of the shellsprovides for a level of standardization and quality control level thatis difficult to obtain economically in a “built-onsite” system.

In another embodiment of the invention, the shells which form the basicconstruction elements of the proposed invention structure may befabricated by preforming the shell members into desired configurationswhich are based on the inverted catenary shape. This shellconfiguration, when implemented in the preferred embodiments, allowsload bearing and dissipation of external forces evenly throughout theshelter structure. During construction phase, the shell members are thensequentially connected and secured together.

In summary, the features of the above-described inventive embodimentsare as follows:

Construction of Shells with Optimal Cross-Section Attributes.

Since the shell structure is built by a well-known industry and reliableforming process variations can be easily made in the constructionprocess to vary the size and complexity of the final product. Differentsized structures can be routinely produced based on varied shell sizeswith the same nominal geometric factors based on the inverted catenaryformulations discussed herein.

Structural Features of the Shell Structure.

A characteristic of the inventive shell structure is that the rigidityand strength of the individual shell members is great and the entirestructure can be significantly reinforced by additional mechanicalelements and processes available in the industry today. These availablemechanical attributes involve steel connectors, post tensionedapparatuses and systems and anchored piers. Because of the combinationof a concrete matrix and reinforced steel rebar, the shell memberseasily resist inward deformation from flying debris impact. Furthermore,the “edge-less” i.e. no sharp edges, nature of the outside shape of theshells with their smooth curves generate minimal wind interference byallowing wind flow past the structure without destructive flow vorticesoccurring on the leeward side of the structure which can destroy orweaken a structure. In addition, the structure is enhanced in theseembodiments by additional mechanisms such as the post tensioned steelcables and specifically designed and buried anchor piers. The netresultant of these novel features illustrates a new invention that iscapable of providing survivability and a level of safety to the peopleduring a major weather event.

The inventive shell structure and the method of construction accordingto the present invention are ideally suited for the mass market sincethe simplicity of construction, economies of scale, and standardizationof design allow construction by non-professional personnel in anenvironment where this type of construction is usually difficult, highlylabor intensive and demanding of a higher level of personnel than thenormal do-it-yourself individual.

The result is an aesthetically pleasing, socially acceptable, safe,strong, extremely protective, comfortable, lightweight, easilytransportable and deployable system that can be implemented andinstalled by workers of average capability and intelligence level,without the need for a high level of professional education andtraining.

On-site assembly is simple and fast using simple tools compared to theconstruction of conventional shelters. Furthermore, by virtue ofsignificant savings in labor and material costs, the shelterconstruction is also cost competitive relative to conventional shelterconstruction.

The features and advantages of subject invention will be furtherunderstood and appreciated by those skilled in the art by reference tothe following written specification, appended drawings and attachedclaims.

PRIOR ART

Two categories of shelters exist. Underground and above ground. Theunderground shelters are basically excavations under grade level andlined with masonry blocks or concrete, or plastic enclosures placed in ahole in the ground and covered with earth. Above ground shelters areeither internal to existing structures or built adjacent existingbuildings. Underground plastic shells, like empty plastic swimming poolsare prone to being expelled from the ground by water movement or shallowwater tables.

Above ground shelters like the “Oz”, Ref.1, which is a massivemonolithic cement structure which are poured around forms placed onlocation. A 5×5 foot structure weighs 21 tons or 42,000 lbs., and costsabout $9,000; an 8×5 structure weighs 60,000 pounds and costs close to$12,000 or more. This is an extraordinarily large quantity of concretefor a simple structure. The total weight of the structures illustratedin the inventive process taught herein is about 12,000 lbs. Thisstructure weight is less than 30% of the weight of comparable structuresavailable commercially today. The material utilized in one currentlyavailable structure can presumably make three structures of the typeillustrated herein.

Furthermore, an elaborate and costly construction operation is needed toimplement the existing types of shelter on location, including the useof massive trucks and cranes and hydraulic systems to transport andinstall these structures. Fences are removed, backyards are destroyed,electrical lines are removed, replaced and re-routed to allow ingressand egress from the building site. Since the shells 1 in this subjectinvention weigh only several hundred pounds, they can easily be“man-handled” by two people at a given construction site with basicconstruction equipment. Underground systems are usually constructed bybackhoe operations which excavate suitable sized holes in the groundinto which the structure is dropped or manually installed. The structureis then covered with earth. A continuing danger in some undergroundsystems is the possibility of collapse due to soil encroachment or waterinvasion is some active soils.

U.S. Pat. No. 4,676,035 teaches a wall construction formed from aplurality of pre-cast reinforced concrete building panels each of whichincludes interior and exterior faces defined peripherally by upper andlower end edges and opposed side edges extending there-between. With animproved welded joint provided between two adjacent side edges of twoadjacent side-by-side panels.

U.S. Pat. No. 4,680,901 teaches a domed self-supporting frame-lessbuilding structure includes a plurality of concrete panels arranged suchthat the panels are under compressive loadings in both the longitudinaland lateral directions. A plurality of circumferential courses of suchpanels are provided with the panels of any one such course being inabutting end-to-end relation with the panels of the next adjacentcourse. A tension ring surrounds the lower extremity of such dome andthe lowermost ends of the panels of the lowermost course are in abuttingrelation with the ring thereby to assist in securing the panels togetherin the abutting edge-to-edge relationship.

US20090025307 describes a composite severe storm structure utilizingpreformed concrete shells and tensioning members.

U.S. Pat. No. 7,765,746 teaches a spheroid shaped dome house made up ofa plurality of complicated spring loaded tiles, attached to thefoundation and mutually connected by means of horizontally andvertically disposed elongate members extending through lumens inadjacent tiles.

U.S. Pat. No. 7,237,363 teaches a domed building or mold constructedwith flexible, lightweight curved panels snapped together using groovesand ridges formed in the panels to form a building wall, a tension ringholding the panels in place and a top cap overlying and secured to upperedges of the panels.

U.S. Pat. No. 6,324,791 teaches a prefabricated but in modules, of thekind that has four sides, two similar sides, a lower one and an upperone, where the cross sections of the module, viewed from the inside, areconcave in the areas close to the lower side and convex in the areasclose to the upper side, with an intermediate area where there is aprogressive change in curvature.

U.S. Pat. No. 5,146,719 teaches a space tension chord arch member domereinforced with tension members and method of construction. Maximumbuilding space is ensured by using tension chord members, which reducesthe material costs and simplifies assembly of the dome. The systempermits use of laminated wood for the arch members of the domesuperstructure.

U.S. Pat. No. 4,313,902 teaches a prestressed concretepressure-containment vessel having one or more cavities within itsexternal shell. The cavities, whether cylindrical or other shape, aretotally contained by prestressing tendons, which apply forces to containvarious pressures within the structure. The invention allows very highinternal pressures to be contained therein.

FIGURES

FIG. 1: Generalized overview graphic of structure showing overall shapeand major components.

FIG. 2 a: Vertical cross-section of structure.

FIG. 2 b: Vertical cross-section showing the inverted catenary form ofthe concrete shells of the structure.

FIG. 3 a: Horizontal cross section showing interlocking concrete shells,dovetailed fitting of adjacent shells, steel tensioned tendons andtendon anchor locations.

FIG. 3 b: Horizontal structural cross-section showing interlockingconcrete shells and recesses in shells for connector flanges in adjacentconcrete shells.

FIG. 4: Horizontal cross-section showing door location in a specificconcrete shell.

FIG. 5: Schematic showing the steel matrix elements of rebar and theupper strengthened steel support flange, the connector flanges betweenadjacent concrete shells and the shell connections to the buriedreinforced piers by an “L-shaped” steel connector.

FIG. 6: Schematic of the outside of structure showing the protective topcap and the hinged door.

FIG. 7 a: Top view of steel flange connecting two adjacent concreteshells.

FIG. 7 b: Front view of steel flange connecting two adjacent concreteshells, located in the recessed space between 2 adjacent concreteshells.

FIG. 7 c: Side view of steel flange in the recessed space between 2concrete shells along with the connecting bolts in the flange.

FIG. 8: Torque sequencing diagram for nuts on the flanges in shellconnections.

FIG. 9: Illustrates the optimal seating arrangement in the shelter.

TABLE 1 Item List Description  1 Concrete shell  2 Structure cap  3Upper steel flange  4 Reinforced metal bar - rebar  5 Steel Flange  6Pier anchor metal flange  7 Hole Excavated for Pier  8 Earth  9 BuriedPier  9a Pier rebar 10 Floor 11 Bench seat assembly 12 Door 12a Doorhinge 13 Lower tension tendon 14 Upper tension tendon 15 Reinforcedconcrete matrix material 16 Dovetail fitting 17 Recess in Shell forflange assembly 18 Tension Anchor in shell 19 Steel connecting bolts 20Channel for tendon cable

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The present invention utilizes pier anchored reinforced concrete shellscomprised of high strength cement with reinforced steel bars calledrebar and tensioned structural elements as a means of imparting posttensioning stress into the structure. Typically, the reinforced concreteshells are prefabricated at an offsite location with conventionalforming processes optimized for maximum cost efficiency and structuralstrength. The dimensions of the reinforced concrete shells can be varieddepending on the height of the structure. Each shell is designed tosimultaneously withstand all expected load stresses made by flyingdebris impacting the structure and the forecasted wind load effects onthe structure during the severe storm weather events.

In the preferred embodiment, the generalized shape of the reinforcedconcrete shell is an inverted catenary curve. These reinforced concreteshells are designed with a plurality of connector means such that theconcrete shells can be firmly anchored to each other laterally andadditionally; connecting means to anchor the shells at ground level; andalso further additionally to a reinforcing means at the top portion ofthe concrete shells thereby forming an integral assembly. This integralassembly is then later post tensioned.

In the present invention the reinforced concrete shells are generallymanufactured in a factory-like setting by methods well known in theindustry. These methods customarily involve placing cementitiousmaterial into forms containing a steel rebar matrix which makes up theinternal tensile support, and allowing the cement to reach its maximumcured strength before the shells are removed and are installed onlocation.

Referring to FIG. 1 which shows the generalized view of a preferredembodiment of the invention; a plurality of specially designedreinforced concrete shells 1 are disposed and connectedcircumferentially to each other and vertically to a plurality of buriedreinforced concrete piers 9. These piers 9 can be implemented inpractice with or without footings depending on the soil type and soilproperties. The shells 1 which are shown in FIG. 2 a are constructedwith a pre-determined cross-section which follows an inverted catenaryshape. This preferred embodiment construction process of utilizing acatenary shape in the shells 1 allows for maximum structural strength,minimum structural wind load effects along with minimum material use inconstruction. By minimizing material usage, the cost of implementationand construction of this type invention can be minimized. These shells 1are connected to the piers 9 physically by connector devices 6 which areattached by secure means that are well known in the construction art.

The piers 9 comprise reinforced concrete elements with multiple steelrebar elements buried at sufficient depths in the earth 8 to withstandall expected overturning wind loads. As shown in FIGS. 3 a, 3 b, theseshells 1 “dovetail” or fit conformably into each other laterally by aplurality of means such that a strong unobstructed surface connection ismade between adjacent shells 1. The “dovetail” fitting 16 is representedvertically in FIG. 3 b.

Referring to FIGS. 2 a, 2 b, a plurality of tensioning devices 13,14 aredisposed internally in each shell 1 to circumferentially provide a meansfor post-tensioning the structure by exerting tensioning forces whichare applied to the shells 1 by means of these tendons 13,14. In apreferred embodiment, the suggested tensioning means are steel tendons13,14 which are anchored in preferred locations 18 which are recessed inspecifically selected origin and anchor shells 1. These tendons 13, 14extended inside the shells 1 from an origin point to the endpoint of thesubject tendons 13, 14.

Also shown in FIG. 2 a is a major reinforced support element in the formof a circular steel flange 3 which is bolted to and connects the topsections of each shell 1 to provide integral rigidity, stiffness andincreased strength to the overall structure. A protective structural cap2 is attached by securing means to the top of the flange 3.

By referring to FIGS. 3 a, 3 b the preferred embodiment illustrates thetapered nature of the edges of the shells 1. This tapered design whichcomprises a wider dimension at the outer shell surface compared to theinner shell surface allows the shells 1 to not only resist the externalforces on the shells 1 but each shell 1 behaves as a “key stone” in thestructure since compresses forces are transferred laterally anduniformly across all the shells 1 in the structure. This “keystone”effect further strengthens the structure.

By referring to FIG. 2 a, the inverted catenary shape of the shells 1 isillustrated. Each of these shells 1 is constructed over a frame of steelrebar 4 herein called a steel matrix, which is surrounded by concretematerial 15 in a manner that is standard in the industry for reinforcedconcrete shell construction. By referring to FIG. 3 a, the preferredembodiment illustrates a plurality of shells 1 which fit together toform the structure and it also shows the tension anchors 18 in therecess 17 in the selected shells for the tensioning tendons 13, 14. Thenecessary hardware for anchoring the tendons 18 is positioned in theserecesses 17. The edges of the shells 1 are tapered inwards as shown inthe illustrations 3 a, 3 b to allow a better fit and more uniformloading laterally. In a departure from typical existing sheltertechnology, the present invention with the preferred embodimentimplements a plurality of internally disposed steel tendons 13, 14 whichprovide considerable supplementary additional forces actingcircumferentially to strengthen the structure. These tendons also showngraphically in FIG. 1 are standard industry devices which have been usedin bridge construction and in large concrete dome structures worldwide.These tendons are internally disposed in each shell 1. It iscontemplated that the multiple tendons 13, 14 are inserted inpre-installed plastic or metal channels 20 in each shell during thefabrication process of shells 1. The tendons 13, 14 in the preferredembodiment are tensioned in excess of 20,000 psi stress.

In the preferred embodiment, FIGS. 7 a, 7 b, 7 c, illustrate theimplementation of the connections between adjoining shells 1. FIG. 7 aillustrates a recessed space 17 in the wall of the shell 1. In thisrecessed space 17, the flange elements 5 are housed. Constructively, amajor rebar element 4 which extends laterally in the shell 1 has a metalflange element 5 welded to the rebar and is nominally at right angles tothe rebar 4. Each rebar 4 has a flange element 5 at each section end.These flange elements 5 are mechanically connected as shown in FIG. 7 bby industry standard methods including welding or by flanged nuts andbolts. FIG. 7 c shows a cross-sectional side view of the recessed space17 wherein the flange 5, the horizontally located rebar 4, theconnecting bolts 19 and the concrete matrix 15 of the shell 1 is fullyillustrated. A plurality of the flanges 5 are implemented in the designand construction to increase the strength of the structure.

FIG. 5 illustrates a preferred embodiment of the invention, in thispreferred embodiment the steel matrix of the shell 1 comprisinghorizontal and vertical rebar elements 4, steel flanges 5, uppercircular flange 3, steel pier connector 6 and steel pier rebar 9 are allintegrally connected to form a stiff system which contributes to theoverall tensile strength and rigidity of the structure.

FIG. 6 is a graphical illustration showing the location of the entry andexit door 12 to the structure. This door 12 which has attachment means,shown by hinges 12 a in this embodiment, comprises a laminated structurewhich has a steel framework and a puncture resistant layer such asKevlar-like fabric or similar resistive material which has beendeveloped in the protective industries for personnel safety duringexplosions. These fabrics are lightweight, widely available with suchnames as “Dragonshield” and are able to resist puncture by flying debrisduring a severe weather event.

FIG. 8 illustrates the preferred embodiment of the tightening sequenceof the flange 5 bolts which maintains maximum structural integrity ofthe subject structure.

It is well known in the lifeboat, rescue and survival industry that acircular shape permits the maximum seating capacity for a given surfacearea. The interior of the structure is shown schematically in FIG. 2 a.A nominally circular bench-like structure 11 is implemented inside thestructure to accommodate a maximum number of people in the given groundspace. FIG. 9 illustrates a typical seating arrangement which allows formaximum capacity with a suitable comfort level in the embodiment of theinvention. The proposed circular design of the subject embodiment allowsfor the most effective use of the available seating space. Federalagencies mandate a specific number of square feet per person within theshelter. For seated individuals 6 square feet are mandated, for standingindividuals 5 square feet of space is required.

As shown in FIG. 9, a typical seating embodiment of this application isshown. For an 8 foot diameter structure with an 8 inch wall thickness itis shown that the outside perimeter is 29.32 feet. The inside area ofthe structure is approximately 50 square ft. Using the area mandated perseated person the subject structure can seat 8 people comfortably. Bycalculating the width provided per individual in this specific structurethe seat width is 42 inches. This number is very comfortable, almostluxurious, compared to the published seating in average airline seats of17.2 inches, in office chairs 20 inches and theater seats 19 inches. Itis therefore, theoretically possible to seat almost 18 people insidethis inventive structure if typical airline seating width are used.

The floor 10 of the structure is covered by any type of durable materialsuitable for outdoor use. Cement floors or wood floors can be used inpractice.

The implementation of this construction method at a given site locationis illustrated by the following sequence of steps. Those familiar withconstruction processes today, can see that modifications can be madewithout departing from the inventive intent of the subject invention.

-   -   1. The selected site location for installation of the structure        is made and the holes for the anchor piers 9 are excavated in        the ground and the steel anchors 9 a are installed with cement.        In some instances pier footings are implemented in the piers 9        under the requisite soil conditions as needed.    -   2. The cement is allowed to cure to maximum strength or for at        least 2 days.    -   3. The structure shelter as illustrated in FIG. 1 is then        assembled by connecting each shell 1 to its pier 9 by the pier        steel connectors 6 and then sequentially aligning the shells 1        by making the flanges 5 fit their neighbor shells 1 correctly.    -   4. After each shell 1 is em-placed on its pier 9, the steel        tendons 13, 14 are connected with the tendon hardware 18        attached to each specific shell 1 by threading the tendon 13,14        inside the shells 1 circumferentially around the structure. The        tendons 13, 14 are inserted in channels 20 which are pre-built        into the shells 1 during forming process. Incrementally, the        tendons 13, 14 are thus inserted into the shells 1.    -   5. The adjacent concrete shells 1 are aligned, connected and        bolted together, but their nuts are not fully torqued after this        initial assembly. All connections shall be fully torqued later        in a specific sequence.    -   6. The structure shells 1 are torqued in a specific sequence        depending on the total number of shells 1. In the preferred        embodiment shown, 8 concrete shells are illustrated.    -   7. After the initial structure assembly in which all nuts are        tightened by hand. The flange 5 bolt nuts are then tightened as        shown by the numbered sequence in FIG. 8. The nuts are tightened        several times by cycling through all shells 1 increasing the        torque incrementally until the recommended torque is achieved.    -   8. For example, the first time around tighten the nuts with a        hand wrench. Second time around tighten the nuts firmly. Third        time around apply approximately 25% recommended torque. Fourth        time apply approximately 75% of recommended torque. Fifth time        around, apply 100% of recommended torque. Continue tightening        nuts all around until nuts do not move under 100% recommended        torque. If possible, re-torque after 24 hours.    -   9. The torque sequence of the shells 1 is designed to allow        maximum load bearing within the structure without creating        additional unbalanced load stresses in the structure which can        be deleterious to its structural integrity.    -   10. The shells 1 are then post tensioned by stressing the        tendons 13, 14 and to their required level of stress. The stress        level is at least 30% of the maximum allowable strength of the        tendon. The post tensioning process is standard for the industry        using hydraulic devices and industry standard anchoring systems.        The anchor systems are recessed into the shells 1 to allow for a        smooth outer surface devoid of debris retention obstructions.    -   11. The door 12 is installed on its specific shell 1 and        anchored to the shell frame.

Further modifications and alternative embodiments of various aspects ofthe invention may be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the invention. It is to beunderstood that the forms of the invention shown and described hereinare to be taken as the presently preferred embodiments.

REFERENCES

-   1. Oz Safe rooms, Del City, Okla.

I claim:
 1. A storm shelter comprising: a plurality of shells having afirst surface with a recess to house a flange, a second surface and athird surface, said shells connected to each other by a connectingmechanism having a member on the shells to strengthen said stormshelter; a structure connected to the second surface of said shells toanchor said shells to the earth to enable said storm shelter towithstand wind load; and a supporter connected to the third surface ofthe shells to support the shells to provide integral rigidity, stiffnessand strength to said storm shelter; wherein said connecting mechanismconnects said shells to each other by connecting said member on saidshells to the flange housed in said recess at an angle to strengthensaid shells by allowing load bearing.
 2. The storm shelter according toclaim 1, wherein said member of the connecting mechanism is connectedperpendicular to the flange housed in said recess.
 3. The storm shelteraccording to claim 1, wherein a connecting edge of said shells connectedto each other is covered by a substance to provide adhesion between saidshells.
 4. The storm shelter according to claim 2, wherein the memberand the flange are connected by a method selected from any one ofwelding and bolting.
 5. The storm shelter according to claim 1, whereinsaid shells are circumferentially connected to each other by theconnecting mechanism.
 6. The storm shelter according to claim 1, whereinsaid structure comprises reinforced concrete with plurality of rebarburied at a depth in the earth.
 7. The storm shelter according to claim1, wherein the structure and the second surface of said shells areconnected by a connecting device.
 8. The storm shelter according toclaim 1, wherein said member is a rebar.
 9. The storm shelter accordingto claim 1, wherein said supporter is a circular flange.
 10. The stormshelter according to claim 1, wherein a covering device covers anopening of said supporter.
 11. The storm shelter according to claim 1,wherein said shells comprise a channel.
 12. The storm shelter accordingto claim 11, wherein said shells are post tensioned by a tensioningdevice to strengthen the shells.
 13. The storm shelter according toclaim 12, wherein said tensioning device is circumferentially coupled tosaid shells.
 14. The storm shelter according to claim 13, wherein saidtensioning device is housed in the channel of said shells.
 15. The stormshelter according to claim 14, wherein at least one of said shells areprovided with a cavity to anchor said tensioning device.
 16. The stormshelter according to claim 1, wherein one of said shells comprises adoor to allow access into said storm shelter.
 17. The storm shelteraccording to claim 16, wherein said door has a resistive layer to enablesaid door to resist puncture by flying debris during weather event. 18.The storm shelter according to claim 1, wherein said storm shelterhouses a sitting arrangement to enable a user to sit.
 19. A method ofconstructing a storm shelter comprising the steps of: Installing astructure on the earth to enable anchoring of said storm shelter;Assembling a plurality of shells having a first surface with a recess,second surface and a third surface by connecting the shells to eachother by a connecting mechanism by connecting a member on the shells toa flange housed in the recess of said first surface at an angle tostrengthen said shells by allowing load bearing; Anchoring said shellsto the structure by connecting said second surface of the shells withthe structure by a connecting device; and Supporting the shells by asupporter by connecting the third surface of the shell to the supporter.20. The method according to claim 19, including assembling the shells byconnecting the member perpendicularly to the flange.
 21. The methodaccording to claim 19, including assembling the shells by covering aconnecting edge of the shells by a substance to provide adhesion betweensaid shells.
 22. The method according to claim 19, including connectingsaid shells circumferentially to each other by the connecting mechanism.23. The method according to claim 19, including installing reinforcedconcrete with a plurality of rebar as the structure to enable anchoringof said storm shelter.
 24. The method according to claim 19, includingcovering an opening of the supporter by a covering device.
 25. Themethod according to claim 19, including post tensioning said shellshaving a channel by a tensioning device housed in the channel.
 26. Themethod according to claim 25, including coupling said tensioning devicecircumferentially to the shells.
 27. The method according to claim 26,including anchoring said tensioning device in a cavity on at least anyon of said shells.
 28. The method according to claim 19, includinginstalling a door on any one of said shells to allow access into thestorm shelter.
 29. The method according to claim 28, includinginstalling a door with a resistive layer to enable the door to resistpuncture by flying debris during weather event.
 30. The method accordingto claim 19, including housing sitting arrangement to enable the user tosit.